1. Field of the Invention
The present invention relates to a rod coating method and apparatus, specifically those in which a web is coated with a coating liquid as a medium for recording images and data such as a magnetic tape, a photo film and printing paper with a coating rod.
2. Description of the Related Art
Methods for forming a coating liquid layer with a desired thickness on a web are a rod coating method (also called a bar coating method), a reverse roll coating method, a gravure coating method, an extrusion coating method, and so forth. The rod coating method is widely used because an apparatus is simple and it can form a thin layer.
The rod coating method is roughly divided into two types. In one type, a coating rod comes into contact with a running web to coat the web with a coating liquid and adjust the amount of the coating liquid. In the other type, a precoating apparatus coats a web with an excessive amount of a coating liquid, and a coating rod comes into contact with the web to adjust the amount of the coating liquid by removing the excess.
The coating rod is a wired coating rod with a wire on its surface, a grooved coating rod with grooves on its surface, or a flat coating rod without the wire and the grooves. The wired coating rod or the grooved coating rod in which a thickness of the coating liquid layer is determined according to a diameter of the wire or a depth of the grooves is generally used; however, those rods are not resistant to abrasion. The flat coating rod is resistant to abrasion since it can be made of an extremely hard metal and there is the coating liquid between the surface of the rod and the web.
Yet, in the rod coating method, the thickness of the layer has a large unevenness along the width of the web as compared with that in the extrusion coating method (the thickness can be adjusted by a slit or the like) since the coating rod does not have a thickness adjusting function. In particular, if the flat coating rod is used, it is difficult to coat the web with a layer thickness unevenness within a regulated range in the width direction of the web because the thickness unevenness of the coating liquid layer in the width direction of the web is easily affected by a thickness unevenness of the web in the width direction of the web itself.
Moreover, the surface of the flat coating rod is close to the web compared with those of the wired coating rod and the grooved coating rod; thus foreign matters are easily caught on the surface of the rod to cause streaks on the layer.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of a rod coating method and apparatus in which a web can be easily coated with a small thickness unevenness of a coating liquid layer in a width direction of the web.
The present invention has been developed in view of the above-described circumstances, and has as its object also the provision of a rod coating method and apparatus in which foreign matters can not be easily caught on a surface of a flat coating rod not to cause streaks on a coating liquid layer.
In order to achieve the above-described objects, the present invention is directed to a rod coating method for forming, with a coating rod, a coating liquid layer on a running web tensioned by a plurality of guide rollers, wherein: the coating rod applies a coating liquid on the web and adjusts an amount of the coating liquid on the web; and the web has a tension variation in a width direction of the web to adjust a thickness unevenness of the coating liquid layer in the width direction of the web.
Moreover, in order to achieve the above-described objects, the present invention is directed to a rod coating method for forming, with a coating rod, a coating liquid layer on a running web tensioned by a plurality of guide rollers, wherein: a precoating apparatus excessively applies a coating liquid on the web and the coating rod adjusts an amount of the coating liquid on the web by removing an excess of the coating liquid on the web; and the web has a tension variation in a width direction of the web to adjust a thickness unevenness of the coating liquid layer in the width direction of the web.
Moreover, in order to achieve the above-described objects, the present invention is directed to a rod coating apparatus for forming, with a coating rod, a coating liquid layer on a running web tensioned by a plurality of guide rollers, comprising: the coating rod which applies a coating liquid on the web and adjusts an amount of the coating liquid on the web; and a moving device which moves at least one of the plurality of guide rollers adjacent to the coating rod.
Moreover, in order to achieve the above-described objects, the present invention is directed to a rod coating apparatus for forming, with a coating rod, a coating liquid layer on a running web tensioned by a plurality of guide rollers, comprising: the coating rod which adjusts an amount of a coating liquid on the web by removing an excess of the coating liquid on the web, the coating liquid having been excessively applied on the web by a precoating apparatus; and a moving device which moves at least one of the plurality of guide rollers adjacent to the coating rod.
In the present invention, the guide roller adjacent to the coating rod is moved to give the tension variation to the web in the width direction of the web. This adjusts the thickness unevenness of the coating liquid layer in the width direction of the web. Therefore, the thickness unevenness of the coating liquid layer in the width direction of the web can be easily reduced. This invention is particularly effective in case of a flat coating rod.
Furthermore, in order to achieve the above-described objects, the present invention is directed to a rod coating method for forming a coating liquid layer on a running web with a flat coating rod, wherein: the flat coating rod applies a coating liquid on the web and adjusts an amount of the coating liquid on the web; and an inequality Rmaxxe2x89xa6h/3 is satisfied where h is a thickness of the coating liquid layer and Rmax is a maximum projection height of a surface of the flat coating rod.
Moreover, in order to achieve the above-described objects, the present invention is directed to a rod coating method for forming a coating liquid layer on a running web with a flat coating rod, wherein: a precoating apparatus excessively applies a coating liquid on the web and the flat coating rod adjusts an amount of the coating liquid on the web by removing an excess of the coating liquid on the web; and an inequality Rmaxxe2x89xa6h/3 is satisfied where h is a thickness of the coating liquid layer and Rmax is a maximum projection height of a surface of the flat coating rod.
Moreover, in order to achieve the above-described objects, the present invention is directed to a rod coating apparatus for forming a coating liquid layer on a running web with a flat coating rod, wherein: the flat coating rod applies a coating liquid on the web and adjusts an amount of the coating liquid on the web; and a surface of the flat coating rod is smoothed so that an inequality Rmaxxe2x89xa6h/3 is satisfied where h is a thickness of the coating liquid layer and Rmax is a maximum projection height of a surface of the flat coating rod.
Moreover, in order to achieve the above-described objects, the present invention is directed to a rod coating apparatus for forming a coating liquid layer on a running web with a flat coating rod, wherein: the flat coating rod adjusts an amount of a coating liquid on the web by removing an excess of the coating liquid on the web, the coating liquid having been excessively applied on the web by a precoating apparatus; and a surface of the flat coating rod is smoothed so that an inequality Rmaxxe2x89xa6h/3 is satisfied where h is a thickness of the coating liquid layer and Rmax is a maximum projection height of a surface of the flat coating rod.
In the present invention, the following inequality is satisfied when the thickness of the coating liquid layer is h and the maximum projection height of the surface of the coating rod is Rmax, Rmaxxe2x89xa6h/3. Therefore, foreign matters can not be easily caught on the surface of the coating rod.